The present invention relates to a surface state monitoring method and apparatus for monitoring surface states of semiconductor wafers, more specifically a surface state monitoring method and apparatus which can monitor surface states of a plurality of semiconductor wafers continuously for a short period of time.
Various requirements at fabrication sites of semiconductor devices require surface states of the semiconductor substrates being accurately grasped.
In the field of semiconductor integrated circuits of memory devices, such as DRAM (Dynamic Random Access Memory), etc., and of logic devices, as a device has higher integration, the gate insulation film at the time of the fabrication of the device is made thinner, and the device has a design that the function for insulating an electric field (about 4xc3x97106 V/cm) of a MOS (Metal Oxide Semiconductor) FET (Field Effect Transistor) in operation has a small margin. Generally, a gate insulation film is formed by thermal oxidation. In forming a gate insulation film by thermal oxidation, in a case of surface contamination, as of metal contamination, chemical contamination, organic contamination or others is present, there is a risk that dielectric breakdown of the formed gate insulation film may be induced. It is known that organic contaminants stayed on the substrate surfaces after the gate insulation film has been formed results in insulation deterioration. Thus, it is very important to form a gate insulation film having dielectric breakdown voltage of a required value that surface states of a semiconductor substrate are administered.
Plasma etching is widely used in steps of patterning device structures. The plasma etching process is determined by dynamic balance in adsorption, reaction and elimination processes between influxes of radical ions, etc. fed in gas phase and outfluxes from semiconductor wafer surfaces. Thus, in the plasma etching process, to set optimum plasma etching conditions and to detect the end point of the plasma etching, it is very effective to know adsorption states, chemical bonding states, structures and thicknesses of reaction layers, etc. of surface states of semiconductor wafers.
Recently, semiconductor devices have elements increasingly micronized, and are made increasingly three dimensional. This makes it difficult for cleaning solutions to intrude into micronized regions or steep steps or to be replaced there. In consideration of future further micronization, dry cleaning is noted. For example, to remove organic contaminants staying on silicon wafers reaction with ozone or oxygen excited by UV radiation is effective. Oxygen molecules are dissolved to oxygen atoms by light of a below 242 nm wavelength. The organic contaminants are oxidized by the oxygen atoms and solved into H2O, O2, CO, CO2, etc. of high vapor pressures. Organic bonds, such as Cxe2x80x94C, Cxe2x80x94H, Cxe2x80x94O, etc. can be dissolved by UV radiation. Thus, knowing surface states of semiconductor wafers is very important also to control parameters for the dry cleaning, such as an optimum amount of radiation, wavelength, oxygen amount, etc.
Native oxide films formed on the surfaces of silicon wafers are not usable in devices because their thickness cannot be controlled. Accordingly, it is preferable that when a device is fabricated on a silicon wafer, native oxide film on the silicon substrate is removed, and silicon bonds on the surfaces are terminated with hydrogen to stabilize the surfaces of the silicon wafer. This is because hydrogen can be eliminated at a relatively low temperature of about 500xc2x0 C., and the termination with hydrogen relatively little affects the following processes. Most of silicon atoms on the surfaces of a silicon wafer subjected to UV ozone cleaning and hydrogen fluoride etching are terminated with hydrogen, and Sixe2x95x90H2 and Sixe2x80x94H are formed. Accordingly, if a state of the- termination with hydrogen on silicon wafer surfaces, temperature dependency of the elimination of terminating hydrogen can be monitored, the silicon wafer surfaces at the start of semiconductor processing can be kept in a suitable state. Higher quality and higher yields can be expected.
Thus, it is very important to know a surface state of a semiconductor wafer in a fabrication process of a semiconductor device, and various monitoring methods and apparatuses have been proposed and locally practiced.
Means for monitoring a surface state of a semiconductor wafer by internal multiple reflection of infrared radiation is provided by, e.g., FT-IR (Fourier-transform spectroscopy) apparatus or the special use marketed by Perkin-Elmer Co., U.S.A. For wider applications of the means Graseby Specac Limited, for example, markets various accessories.
In the conventional surface state monitoring method using this means, as exemplified in FIG. 13A, a substrate-to-be-monitored 102 is cut into, e.g., a 40 mmxc3x9710 mm strip, and infrared radiation emitted from an infrared radiation source 104 is passed through the substrate-to-be-monitored 102 to monitor states of the substrate surfaces. Otherwise, as exemplified in FIG. 13B, a substrate-to-be-monitored 102 has the end tapered, and infrared radiation is incident on the end surface of the substrate-to-be-monitored 102 to undergo multiple reflection inside the substrate, whereby a surface state of the substrate is monitored. Otherwise, as exemplified in FIG. 13C, infrared radiation is incident on a substrate-to-be-monitored via a prism 106 positioned above the substrate to undergo multiple reflection inside the substrate, whereby a surface state of the substrate is monitored.
The basic principle of monitoring a surface state of a substrate by applying infrared radiation to a substrate to cause the infrared radiation to undergo internal multiple reflection is as follows. When the frequency of an evanescent wave oozing when the infrared radiation reflects on the surface of the substrate agrees with the molecular vibrational frequency of the organic contaminants on the substrate surface, the specific frequency component of the infrared radiation is resonance-absorbed. Thus, kinds and amounts of the organic contaminants can be determined by measuring the spectra of the infrared radiation. The basic principle also has a function that information of organic contaminants on substrate surfaces is gradually made more exact. A signal vs. noise ratio (S/N ratio) is also improved.
However, these monitoring methods needs cutting a substrate-to-be-monitored into strips, additionally machining a substrate-to-be-monitored, or disposing a prism above a substrate-to-be-monitored. These monitoring methods have not been usable in the in-situ monitoring at site of fabricating semiconductor devices.
Methods of monitoring organic contaminants on semiconductor substrates are known thermal desorption GC/MS (Gas Chromatography/Mass Spectroscopy), APIMS (Atmospheric Pressure Ionization Mass Spectroscopy), TDS (Thermal Desorption Spectroscopy), etc. However, these methods are not suitable to be used in in-situ monitoring at site of fabricating semiconductors for reasons that these methods cannot directly observe large wafers of, e.g., above 300 mm-diameters which are expected to be developed, and need vacuum ambient atmosphere, and have low throughputs, and other reasons.
As described above, the above-described conventional surface state monitoring methods are not usable in the in-situ monitoring at site of fabricating semiconductor devices because the monitoring by these method is destructive, or these methods are not suitable for monitoring large semiconductor wafers. Surface state monitoring methods and apparatuses which permit the in-situ monitoring of substrate surfaces at site of fabricating semiconductor devices, and permit large wafers to be monitored have been expected.
In view of the above, the inventors of the present application have already proposed an organic contaminant detecting method using wafer internal multiple reflection Fourier transformation infrared spectroscopy (see, e.g., the specification of Japanese Patent Application No. 95853/1999). When infrared radiation is applied to one end of a wafer at a specific incidence angle, the infrared radiation propagates inside the wafer, repeating total reflections on both surfaces. The infrared radiation oozes the surfaces of the wafer (evanescent waves), and a part of infrared spectra is absorbed by organic contaminants staying on the surfaces. The propagated infrared radiation emitted at the other end of the wafer is spectroscopically analyzed by FT-IR to thereby detect and identify the organic contaminants staying on the surfaces of the wafer. This monitoring method has sensitivity equal to GC/MS, and in addition thereto the monitoring has realtime, and simple and economical.
In the surface state monitoring method described in the specification of Japanese Patent Application No. 95853/1999, the offset shape of a wafer is used to induce infrared radiation into the wafer at the declined part of the peripheral edge of the wafer. Accordingly, it is not necessary to machine the semiconductor wafer itself, which permits the in-situ monitoring in the process for fabricating a semiconductor device.
However, in the respective fabrication steps of a semiconductor device mass-production line, the process is generally conducted by a single wafer processing. Thus, it takes time to monitor a plurality of wafers sequentially wafer by wafer in the wafer monitor following the processing, which affects throughput of the fabrication steps as a whole. To administer production throughput per rot, monitor results or statistic monitoring per rot is necessary. Also to this end, it is a significant problem that the monitor of each wafer takes less time.
An object of the present invention is to provide a surface state monitoring method and apparatus which can monitor a plurality of wafers continuously and for a short period of time.
The above-described object is achieved by a surface state monitoring apparatus comprising: a wafer cassette holding a plurality of semiconductor wafers; an incidence optical system for applying infrared radiation to at least one of said plurality of semiconductor wafers; a detection optical system for detecting infrared radiation which has undergone multiple reflection in the semiconductor wafer and exited from the semiconductor wafer; surface state monitoring means for monitoring surface states of the semiconductor wafer, based on the infrared radiation detected by the detection optical system; and displacing means for displacing the wafer cassette relative to the incidence optical system and the detection optical system, surface states of-said plurality of semiconductor wafers being sequentially monitored while the wafer cassette is displaced relative to the incidence optical system and the detection optical system by the displacing means, whereby surface states of said plurality of semiconductor wafers held in the wafer cassette are continuously monitored.
The above-described object is achieved by a surface state monitoring apparatus comprising: a wafer cassette holding a plurality of semiconductor wafers; an incidence optical system for applying infrared radiation to at least one of said plurality of semiconductor wafers; a detection optical system for detecting infrared radiation which has undergone multiple reflection in the semiconductor wafer and exited from the semiconductor wafer; and surface state monitoring means for monitoring surface states of the semiconductor wafer, based on the infrared radiation detected by the detection optical system, the incidence optical system being controlled to apply the infrared radiation sequentially to said semiconductor wafers, whereby surface states of said plurality of semiconductor wafers held in the wafer cassette being continuously monitored.
The above-described object is achieved by a surface state monitoring apparatus comprising: a wafer cassette holding a plurality of semiconductor wafers; an incidence optical system for applying infrared radiation to at least two or more of said semiconductor wafers; a detection optical system for collectively detecting infrared radiations which have undergone multiple reflection in the semiconductor wafers and exited from the semiconductor wafers, respectively; and surface state monitoring means for monitoring surface states of the semiconductor wafers, based on the infrared radiations detected by the detection optical system.
In the above-described surface state monitoring apparatuses, it is possible that the apparatus further comprises: displacing means for displacing the wafer cassette relative to the incidence optical system and the detection optical system.
The above-described object is achieved by a surface state monitoring method comprising: applying infrared radiation to at least one of a plurality of semiconductor wafers held in a wafer cassette, detecting infrared radiation which has undergone multiple reflection in the semiconductor wafer and exited from the semiconductor wafer, and analyzing the detected infrared radiation to monitor surface states of the semiconductor wafer, surface states of the semiconductor wafer being monitored while the wafer cassette is displaced relative to an infrared radiation optical system to continuously monitor surface states of said plurality of semiconductor wafers held in the wafer cassette.
In the above-described surface state monitoring method, it is possible that the wafer cassette is intermittent displaced wafer by wafer relative to the infrared radiation optical system.
In the above-described surface state monitoring method, it is possible that the wafer cassette is continuously displaced relative to the infrared radiation optical system.
In the above-described surface state monitoring method, it is possible that a displacement of the wafer cassette relative to the infrared radiation optical system, and a monitor of surface states of the semiconductor wafer are synchronized with each other.
The above-described object is achieved by a surface state monitoring method comprising: applying infrared radiation to at least one of a plurality of semiconductor wafers held in a wafer cassette, detecting infrared radiation which has undergone multiple reflection in the semiconductor wafer and exited from the semiconductor wafer, and analyzing the detected infrared radiation to monitor surface states of the semiconductor wafer, an infrared radiation optical system being controlled to apply infrared radiation sequentially to a different one of said plurality of semiconductor wafers, whereby surface states of said plurality of semiconductor wafers held in the wafer cassette are continuously monitored.
In the above-described surface state monitoring method, it is possible that a control of the infrared radiation optical system and a monitor of surface states of the semiconductor wafer are synchronized with each other.
The above-described object is achieved by a surface state monitoring method comprising: applying infrared radiation to respective at least two or more of a plurality of semiconductor wafers held in a wafer cassette; collectively detecting infrared radiations which has undergone multiple reflection in the semiconductor wafers and exited from the semiconductor wafers, respectively; and analyzing the detected infrared radiation to monitor surface states of the semiconductor wafers.
In the above-described surface state monitoring method, it is possible that surface states of said plurality of semiconductor wafers held in the wafer cassette are collectively monitored.
According to the present invention, surface states of semiconductor wafers can be discontiguously and non-destructively monitored continuously and for a short period of time, held in wafer cassettes. Means for storing monitored data for each wafer is provided, whereby wafers can be monitored not only sheet by sheet but also in the unit of a wafer cassette. The monitored data can be utilized for statistic administration of fabrication yields.